The present invention relates to a method of modifying the property of a polymeric material. More particularly, the invention relates to a method to improve the properties such as water absorption and adhesion, etc. of a polymeric material without lowering the practical strength of the material.
Because polyolefins such as polypropylene, polyethylene, etc. have excellent properties of light weight, large strength, good chemical resistance, etc., they are extensively used for films, non-woven fabrics, molded materials for automobile components and members of electrical apparatus, etc. On the other hand, polyolefin materials have a small polarity and a high crystallinity, which are derived from its chemical structure, thus they have a small hydrophilic property and a difficulty in chemical modification. Various surface activation treatments such as ozone treatment, plasma treatment, ultraviolet light irradiation, high voltage electric discharge, corona discharge, etc. have been carried out to improve the hydrophilic property and adhesive property of polyolefin materials. However, even if any method of them is employed to treat a polyolefin material, we cannot obtain an effective result that the treated material absorbs water as much as several times the weight of original material.
Various kinds of treatments have been proposed in order to improve the property of polymeric materials such as polypropylene, etc. For examples, the ozone oxidation treatment was examined to improve the property of metal plating, painting and adhesion (Japanese Laid-Open Patent Publication No. H3-103448 (1991)). However, when only the ozone treatment is employed to improve the property of the material, it needs very strict conditions which cause the lowering of the mechanical strength; this makes a problem that the treatment is not practical. Furthermore, it is impossible to give a large water absorption property to the material only by the ozone treatment.
Furthermore, it was proposed that vinyl monomers containing ester bonds were grafted to non-woven fabrics made of polyolefin and then, the ester bonds were hydrolyzed to form acid groups giving a hydrophilic property and an ion-exchange property (Japanese Laid-Open Patent Publication No. H11-7937 (1999)). However, the grafting of vinyl monomers to polyolefin to give a large hydrophilic property is not easily carried out by the proposed method. Still more, the method needs the hydrolysis treatment after the grafting, which causes a laborious problem.
On the other hand, a method to improve a hydrophilic property of non-woven fabrics made of polyolefin fibers by the treatment with hydrophilic resin in the presence of a persulfate was proposed (Japanese Laid-Open Patent Publication No. H11-67183 (1999)). Although this method gave practically a hydrophilic property to non-woven fabrics, the hydrophilic property is not durable in use. In addition, this method was not applicable for the improvement of hydrophilic property and adhesion property of films and molding materials except non-woven fabrics. For instance, the hydrophilicity given by this method is considerably lost by washing with a hot detergent solution.
It is known that a method to improve a hydrophilic property of non-woven fabrics by coating them with polyvinyl alcohol (Japanese Laid-Open Patent Publication No. H1-248460 (1989)). Although the hydrophilic property of the treated non-woven fabrics is high, its durability is very low because the treatment is only coating. In addition, the coated non-woven fabrics give a disadvantage in that when they are used as battery separators, they shrink and cause short-circuiting in the batteries.
The present inventor proposed a method to improve the surface property, or especially, the dyeability of polymeric materials, which is composed of activation treatment of the surface of polymeric materials, monomer grafting such as acryl amide, etc. on them and Hofmann rearrangement of the amide groups in grafts (Japanese Laid-Open Patent Publication No. H8-109228 (1997)). Although this method is available for improving the hydrophilic property of some polymeric materials, the kind of available polymeric materials is limited.
The present invention provides a method for improving a durable water absorption property, a hydrophilic property and an adhesion, etc. for a polymeric material without lowering the practical strength. The present invention also provides medical/sanitary/cosmetic supplies; disposable diapers, sanitary or other napkins, bandages, gauze and disinfectants and various water-absorption materials for cleaning, cleanser pack, etc., water retention materials useful for agriculture/greening in dry districts, materials for microorganism culture media, synthetic paper, filter media, battery separators with alkali/acid proofing, members of writing materials with an excellent absorption property of water-soluble ink, wiping/cleansing materials, orthodontic brackets, medical materials (artificial organs, artificial joints, medical tubes and the other molded materials with string or plate forms), polymeric materials with improved adhesive property and polymeric materials for composites.
The present inventor investigated the method for improving the property of polymeric materials such as a water adsorption property, a hydrophilic property, and an adhesion property, etc. and discovered that a combination of a solvent treatment, an activation treatment, a hydrophilic polymer treatment and a monomer grafting is effective for the improvement, and completed the present invention.
A first aspect of the present invention relates to the method for improving polymeric materials by (1) the step of activation-treatment and (2) the step of a hydrophilic polymer-treatment in this order.
A second aspect of the present invention relates to the method to improve polymeric materials by (1) the step of activation-treatment and (2) the step of a hydrophilic polymer-treatment and (3) the step of monomer grafting in this order.
A third aspect of the present invention relates to the method to improve polymeric materials by (1) the step of a solvent-treatment, (2) the step of activation-treatment and (3) the step of a hydrophilic polymer-treatment in this order.
A fourth aspect of the present invention relates to the method to improve polymeric materials by (1) the step of a solvent-treatment, (2) the step of activation-treatment, (3) the step of a hydrophilic polymer treatment and (4) the step of monomer grafting in this order.
The present invention also relates to the products prepared from the polymeric materials improved by the above methods; a water absorption material, a water retention material, a material for microorganism culture media, a synthetic paper, a filter medium, a battery separator, a member of writing materials (members made of polymer used for various kinds of pens with water-soluble ink, felt pens, brush pens, fountain pens and ball-point pens, etc.), a wiping/cleansing cloth, a disposal medical/sanitary/cosmetic supply (a diaper, a sanitary napkin, a bandage, a gauze, the other medical/sanitary supply and various cosmetic supplies for cleaning/cleansing pack), a material improved in adhesion property, an orthodontic bracket, a medical material (an artificial organ, an artificial joint, a medical tube and the other molding material of tube, string or plate), etc.
The present invention will be described in more detail. (Polymeric materials)
Polymeric materials used in the present invention include the polymer material contained in each of a single polymer or a mixture of synthetic or natural polymers, a modified single polymer or polymer mixture, a material prepared by mixing or conjugating the polymers with glass, metal and carbon fiber, etc.
Both thermoplastic polymers and thermosetting polymers are used as synthetic polymers. Various methods for the preparation of these polymers are exemplified, and all polymers prepared by these methods can be used. For example, the following polymers are available; (1) polymers made by an addition polymerization; homopolymers or copolymers prepared by the polymerization of a single kind of monomer or a mixture of monomers selected from olefins, vinyl compounds except olefins, vinylidene compounds, the other compounds with Cxe2x95x90C double bonds, (2) polymers made by polycondensation; a polyester and a polyamide, etc. or their mixture or modified polymers, (3) polymers made by addition polycondensation; phenol resin (containing Kynol (commercial name of Japan Kynol Co., Ltd.), urea resin, melamine resin, xylene resin, or their mixture or modified polymers, (4) polymers prepared by polyaddition; polyurethane, polyurea, and these mixture or modified polymers, (5) polymers prepared by the ring-opening polymerization; a homopolymer or a copolymer prepared by cyclopropane, ethylene oxide, propylene oxide, lactone and lactam, and these mixtures or modified polymers, (6) cyclic polymers; polymers prepared by the polymerization of divinyl compounds (e.g., 1,4-pentadiene) or diyne compounds (e.g. 1,6-heptadiyne) and these mixture or chemically modified polymers, (7) polymers prepared by isomeric polymerization; e.g., alternative copolymer of ethylene and isobutene, (8) polymers prepared by the electrolytic polymerization; a homopolymer or a copolymer prepared by pyrrole, aniline and acetylene, etc. and their mixture or chemically modified polymers, (9) polymers made of aldehydes and ketones, (10) poly(ethersulfone) and (11) polypeptides.
A single material or a mixture of cellulose, proteins and polysaccharides or these derivatives, etc. are given as natural polymers.
In the present invention, the polymers made by an addition polymerization described above are preferably used. Monomers used in an addition polymerization are not specially limited. A homopolymer or a copolymer of xcex1-olefins such as ethylene, propylene, butene-1, pentene-1, hexene-1,4-methylpentene-1, octene-1, etc. are used.
In the present invention, vinyl compounds except olefins give the compounds with vinyl groups. For instance, the following compounds are given; vinyl chloride, styrene, acrylic acid, methacrylic acid, esters of acrylic or methacrylic acids, vinyl acetate, vinyl ethers, vinyl carbazole, and acrylonitrile, etc.
As compounds except olefins compounds containing vinylidene groups; vinilidene chloride, vinilidene fluoride and isobutylene are exemplified.
As the compounds with carbon-carbon double bonds except olefins, vinyl compounds and vinilidene compounds, the following compounds are given; maleic anhydride, pyromellitic dianhydride, 2-butene acid, tetrafluoroethylene, chlorotrifuluoro-ethylene, etc. and compounds with two or more vinyl groups, for instance, butadiene, isoprene and chloroprene, etc.
As preferable polymers made by the addition polymerization, homopolymers or copolymers of two or more monomers selected from these monomers or a mixture of these polymers can be suitably used. Especially preferable addition polymers are polyethylene, a copolymer of ethylene and the other xcex1-olefin, polypropylene, a copolymer of propylene and the other xcex1-olefin. These copolymers represent both of random copolymers and block copolymers. As the present invention is effective for the improvement of the hydrophilic property of polyolefins, which is especially difficult for a chemical treatment, polyolefins are preferably used.
As polymeric materials other than polyolefins, homopolymers or copolymers of monomers selected from vinyl compounds, vinylidene compounds or compounds with carbon-carbon double bonds; poly(methacrylate)s, poly(acrylate)s, polystyrene, poly tetrafluoroethylene, copolymers containing acrylonitrile (acrylic fiber and its molded product and ABS resin, etc.) and copolymers containing butadiene (synthetic rubber), etc., polyamides (contain-ing nylon and aliphatic or aromatic polyamides), polyesters (containing polyethylene terephthalate and aliphatic or all-aromatic polyesters), polycarbonate, polyurethane, polybenzoate, polyethersulfone, a carbon material such as carbon fiber, etc., various synthetic rubbers, wool, silk, etc. are preferably used.
As the polymers except the above ones, the following polymers are preferably used; poly(phenol) (commercial name, Kynol), poly(alkyl-p-hydroxybenzoate), polyimide, poly(benzimidazole), poly-(p-phenylene benzobisthiazole), poly-(p-phenylene benzbisoxazole), poly(benzothiazole), poly(benzoxazole), and the following fibers are preferably used; cotton, flax, hemp, ramie, jute, and other vegetable fibers, animal hair fibers except wool, cellulose acetate, regenerated cellulose (rayon, cupra, polynosic, etc.), vinylon, a copolymer of vinylalcohol and vinylchloride (polychlal; commercial name, Cordera) and casein fiber. In addition, mixtures or composites of these polymeric materials are preferably available.
The polymeric materials are not limited to the above exemplified ones but any of other polymers may be used for the present invention.
It is possible to improve the polymeric materials containing antistatic agents, stabilizers, nucleation agents, flame retardants, foaming agents and various additives which are usually added in polymeric materials by the present invention.
In the present invention, the form of polymeric materials to be improved is not limited. For instance, each of fiber, a woven fabric, a non-woven fabric, a cloth, a plate, a film, a tube, a rod, a hollow container, a case, a foamed material and a laminate is available. Especially, the water absorption property of fibers, woven fabrics, non-woven fabrics, cloth, films, and sheets can be easily improved. Porous films and sheets prepared for filtration mediums or synthetic papers are easily improved in a durable water absorption property. In addition, by improving members/parts of materials molded previously in a desired form, the polymeric materials which had not been used are enabled to be useful. For instance, when members of writing materials (ink holders, brushes of brush pens, felt-pens, autograph pens, ink-collector, etc.) made of polyolefins, polyesters and ABS resin are treated by the present method, the obtained members/parts become wettable with water-soluble ink and the performance of the writing materials can be advanced. When the other plastic materials (volts, nuts, chains, parts of electronics, caps, covers, etc.) are treated by the present method, their wettability and adhesion property are improved and the electrification is decreased.
Among fibers and fiber products, for instance, a polyolefin fiber, a polyester fiber, an acrylic fiber, a polyurethane fiber, a polyamide fiber such as nylon and polyaramide, a polyvinyl chloride fiber, a carbon fiber, silk, wool, etc. or woven fabrics and non-woven fabrics of these fibers are preferably used. Each form of fibers is available; a single kind of fiber, a mixture of two or more kinds of fibers, a mixed spinning fiber and a conjugate fiber (a sheath-core type fiber, a side-by-side aligned fiber, a multi-core fiber, an island-in the-sea type (archipelago type) and a hollow-segment-pie fiber, etc.).
(Activation Treatment Process)
In the present invention, the activation treatment process is to introduce functional groups containing oxygen or nitrogen, etc. or unsaturated bonds into the surface of the polymeric materials by various treatments such as ozone treatment, ultraviolet light irradiation treatment, discharging process, etc. It is not necessary to put vinyl monomers or other organic compounds in this process.
The extent of the activation treatment is not especially limited; it depends on the purpose of the treatment. An infrared spectroscopy is employed to see the extent of the activation treatment. For example, a ratio of the absorbance due to carbonyl groups introduced in materials to that due to the crystalline region which is not changed by the treatment is estimated by the base line method and it is used to see the extent of the oxidation by the activation treatment.
In the present invention, observing the absorbance due to carbonyl groups before and after the treatment, the extent that a trace of the formation of carbonyl groups is made sure, which suggests an oxidation, is enough and preferable for the activation treatment. For instance, in the case of polypropylene, it is preferable that the ratio of the absorbance at around 1710 cmxe2x88x921 due to the carbonyl groups introduced in the polymer to the absorbance at around 973 cmxe2x88x921 due to the methyl groups unchanged in the crystalline region is about 0.2 or less.
It is preferable that the polymeric materials are washed with appropriate solvents to remove the impurities before the activation treatment. For instance, polyolefins, polyvinyl chloride and polyvinylidene chloride, etc. are preferably washed with methanol and toluene. Cellulose acetate, nylons, polyesters, polystyrene, acrylic resin, polyvinyl acetate, polycarbonate, polyurethane, etc. are preferably washed with alcohols (methanol or ethanol). It is preferable that cellulose materials such as cotton, hemp, rayon, cuprammonium rayon, etc. are washed with alcohols after washing with detergents.
As a method of activation treatments, each of ozone treatment, plasma treatment, ultra-violet right irradiation treatment, high voltage electric discharge treatment and corona discharge treatment are available.
(Ozone Treatment)
The ozone treatment is to carry out a chemical reaction, mainly oxidation of the surface of polymeric materials with ozone molecules upon contact with ozone in order to improve the polymeric materials.
The ozone treatment is carried out by exposing polymeric materials to ozone. Any methods of ozone treatment are available; for instance, to put a polymeric material under the atmosphere of ozone for a given time or to put a polymeric material in the stream of ozone, etc.
Ozone is produced by passing air, oxygen, or gas containing oxygen such as oxygen-added air through an ozone generator. The ozone treatment is carried out by introducing the obtained gas containing ozone into a reaction vessel or a container in which a polymeric material is involved. The conditions of ozone treatment such as a concentration of ozone in a gas containing ozone, an exposure time and temperature, etc. are appropriately determined considering a kind and form of a polymeric material and the aim of the surface improvement. Usually, an ozone concentration from 0.1 to 200 mg/l, a temperature from 10 to 80xc2x0 C. and a reaction time from 1 minute to 10 hours are applicable. For example, the treatment with the ozone concentration from 10 to 40 g/m3 and a time from about 10 to 30 minutes at room temperature is available for the treatment of polypropylene and polyvinyl chloride fibers. When a polymeric material is a film, a treatment with an ozone concentration of 10 to 80 g/m3 and the time from about 20 minutes to 3 hours is available. When air is used instead of oxygen, the ozone concentration becomes about a half of that with oxygen.
It is considered that hydroperoxide groups (xe2x80x94Oxe2x80x94OH), etc. are formed and some of them are changed to hydroxide groups and carbonyl groups on the surface of a polymeric material by the reaction, mainly oxidation, with ozone treatment.
(Plasma Treatment)
A plasma treatment is carried out to introduce functional groups containing oxygen, nitrogen, etc. to the surface of materials; a polymeric material is put in a vessel containing a gas such as argon, neon, helium, nitrogen, carbon dioxide, oxygen and air, etc. and it is exposed to the plasma generated by a glow discharge. It is considered that radicals are generated on the surface of the polymeric material by the attack of the plasma. Subsequently, the radicals are exposed to air and reacted with oxygen to form carboxylic groups, carbonyl groups and amino groups, etc. on the surface of the polymeric material. The plasma treatment under a low pressure of nitrogen, oxygen or air can produce functional groups directly in the polymeric material.
Methods of the electric discharge are classified in (1) a direct current discharge, (2) a radio-wave discharge, and (3) a microwave discharge.
(Ultraviolet Radiation Treatment)
Ultraviolet radiation treatment is a method to irradiate an ultraviolet (UV) light to the surface of polymeric materials. Low-pressure mercury lamps, high-pressure mercury lamps, super high-pressure mercury lamps, xenon lamps and metal halide lamps are employed as a UV light source. It is effective that a polymeric material is treated with a solvent which can absorb UV light before the UV irradiation. Although any wave length of UV light is available, that of around 360 nm is preferable to decrease the deterioration of the material. The following is considered. When a UV light is irradiated to a polymeric material, a part of the light is absorbed by the chemical structure such as double bonds, etc. in the surface of the polymeric material and some chemical bonds are broken to produce radicals by the absorbed energy. The resulting radicals are considered to produce carboxylic groups or carbonyl groups via peroxides by the bonding of oxygen in air.
(High Voltage Electric Discharge Treatment)
A high voltage electric discharge treatment is as follows. A polymeric material is put on a belt conveyor roller equipped in a tunnel-shaped instrument and the material is carried by the belt. A high voltage such as several hundred thousands volts is put between a lot of electrodes attached to the inner wall of the instrument, which makes an electric discharge in air. It is considered that the electric discharge activates the oxygen in air and the surface of the material, and the oxygen incorporated into the material forms polar groups in the polymeric material.
(Corona Discharge Treatment)
A corona discharge treatment is as follows. A high voltage of several thousands volts is given between a grounded metal roller and knife-shaped electrodes which are aligned in several millimeter intervals to the metal roller. A polymeric material is passed through the space between these electrodes where the corona discharge is generating. This method is suitable for films or thin materials.
The methods except the ozone treatment are based on an energy irradiation. When a polymeric material has a part which makes a shadow for the irradiation, some techniques are necessary to treat the part by the irradiation. Therefore, the ozone treatment is preferable for the treatment of materials such as a non-woven fabric and a fiber-assembled material which gives shadow parts derived from the material""s structure. In addition, the ozone treatment is economical and preferable because of the inexpensive facility
A polymeric material activated by the ozone treatment, etc. is subsequently treated by a hydrophilic polymer treatment. Further more, the material treated by a hydrophilic polymer is treated by a monomer grafting in the Aspects 2 and 4 of the present invention.
(Solvent Treatment)
In order to make the activation treatment more effective, xe2x80x9csolvent treatmentxe2x80x9d is preferably carried out before the activation treatment.
The solvent treatment is to dip a polymer material in a solvent which has a poor solubility of it under the condition that the material is not dissolved in it. A polymeric material is dipped in such a solvent for about 1 minute to 60 minutes at a temperature range of room temperature to about 60xc2x0 C., and the material gives a weight increase of 0.2 to 10% of the original weight without any deformation. This process can be completed by drying the material quickly after dipping in the solvent. The solvent treatment is not always necessary when the polymeric material is a non-woven fabric or fibers. But, this treatment is very effective for the treatment of a material with a small surface area such as films and plates, or for a material containing a considerable amount of antioxidants or other additives. In the case of polypropylene, the material is immersed in a liquid for a solvent treatment (such as toluene, xylene, decalin, tetralin, cyclohexane, etc.) for 1 to 30 minutes in the range of room temperature to 50xc2x0 C., and the surface of the material is dried. Subsequent treatment should be carried out soon after the solvent treatment. As a liquid for the solvent treatment of polyethylene, decalin, tetralin, xylene, and 1-chloro-naphthalene, etc. are effective. For each of the other polymers, a combination of a solvent and a temperature which gives no solubility of the polymer should be examined.
For example, a non-woven fabric made of polyolefin fiber with a circle cross section of a diameter of about 5 to 10 xcexcm is immersed into toluene for 2 minutes at room temperature, and is squeezed, and remaining toluene is removed by a centrifugation. Then, the material is dried by an electric fan; when the toluene on the surface of the material seemed to be evaporated apparently, the solvent treatment is finished. In the case of polyolefin films or plates and the other molded materials, they are immersed in toluene for 10 to 30 minutes at 50xc2x0 C., squeezed as described above, and dried. In these cases, the weight increase is from about 1% to 5%.
(Hydrophilic Polymer)
In the present invention, xe2x80x9chydrophilic polymersxe2x80x9d represents water-soluble polymers or polymers which are not soluble in water but have a hydrophilic property. Specific examples of polymers are as follows; poly(vinyl alcohol), sodium carboxymethyl cellulose, ethylene-vinyl alcohol copolymer, poly(hydroxyethyl methacrylate), poly(xcex1-hydroxy vinyl alcohol), poly(acrylic acid), poly(xcex1-hydroxy acrylic acid), poly(vinyl pyrrolidone), poly(alkylene glycol)s such as poly(ethylene glycol) and poly(propylene glycol), starch such as potato starch, corn starch, wheat starch, etc., glucomannan, silk fibroin, silk sericin, agar, gelatin, egg white, sodium arginate, etc. These sulfonates can also be available.
(Hydrophilic Polymer Treatment)
It is preferable that the hydrophilic polymer treatment of a polymeric material made by the activation treatment is carried out in the presence of catalysts or initiators (generically, they are called xe2x80x9cinitiatorsxe2x80x9d, and used similarly in the monomer grafting).
The following initiators are exemplified; peroxides (benzoyl peroxide, t-butylhydroxy peroxide, di-t-butylhydroxy peroxide, etc.), cerium ammonium nitrate (IV), persulfates (potassium persulfate, ammonium persulfate, etc.), oxidation-reduction initiators (oxidants; persulfates, hydrogen peroxide, hydroperoxide, etc. and inorganic reductants; copper salts, iron salts, sodium hydrogen sulfite, sodium thiosulfate, etc. or organic reductants; alcohols, amines, oxalic acid, etc. and these mixture, and oxidants; hydrogen peroxide, etc. and inorganic reductants; copper salts, iron salts, sodium hydrogen sulfite, sodium thiosulfate, etc., or organic reductants; dialkyl peroxide, diacyl peroxides, etc. and reductants; tertiary amines, naphthenates, mercaptans, organometallic compounds (triethyl aluminium, triethyl boron, etc. and these mixture), the other usual initiators of radical polymerization, etc.
In the hydrophilic polymer treatment process, it is preferable to use a hydrophilic polymer in the solution state. A water-soluble polymer is used as an aqueous solution. When a hydrophilic polymer is not soluble easily in water, it can be used as a solution in an adequate solvent. The use of water-soluble polymers is explained below.
When a treatment with a water-soluble polymer is carried out in the absence of an initiator, a polymeric material finished by the activation treatment is put in an aqueous solution of the water-soluble polymer.
When a treatment with a water-soluble polymer is carried out in the presence of an initiator, first, an aqueous solution of the water-soluble polymer is prepared. Then, if the initiator is water-soluble, a given amount of it is dissolved in the aqueous solution of the water-soluble polymer. If the initiator is not dissolved in water, it is dissolved in an organic solvent such as alcohols or acetone which are miscible with water, and then, the solution is added in the aqueous solution of the water-soluble polymer. Then, a polymeric material finished by the activation treatment is put in the solution of the water-soluble polymer and the initiator. The inner atmosphere of the reaction vessel is desirable to be substituted with nitrogen gas, but the nitrogen atmosphere is not always necessary for a usual treatment.
The temperature is not limited for the treatment with a water-soluble polymer and an initiator, usually, the temperature of 10xc2x0C. to 80xc2x0 C. is available, but that of 60xc2x0 C. to 90xc2x0 C. is more preferable. The treatment for a long period of time (e.g.,.about 12 hours) at a high temperature is preferably carried out in order to obtain a durable hydrophilicity of a polymeric material. A characteristic of the present invention is as follows. Even when the amount of a hydrophilic polymer bound to a polymeric material in the hydrophilic polymer treatment is too small to be analyzed by usual analytical methods, a hydrophilicity of the polymeric material can be effectively improved by the present invention. Besides, as a ratio of a surface area of a polymeric material depends on the kind of the material, for instance, a percentage of weight increase in a treated material is largely dependent on each material. As a molded polymeric material has a small specific surface area, even when the percentage of the weight increase in the treated material becomes a very small value less than 1 wt %, an effective modification can be obtained. In the case of thin films, the percentage of the weight increase in the treated material becomes larger as compared with a thick molded product. In the treatment of a material with a large specific surface area such as a non-woven fabric, the material of a weight increase less than 5 wt % gives an excellent improvement in the hydrophilicity. However, the present invention is not limited by these values.
(Monomer Grafting Treatment)
In the present invention, the monomers for grafting are desirable to have at least one carbon-carbon double bond, for instance, vinyl compounds or similar compounds to them are preferable, although the other monomers which polymerize are available. Hydrophilic monomers are preferable for the present treatment. As hydrophilic monomers, at least a single monomer or a mixture of monomers selected from the following monomers are preferably used; acrylic acid, methacrylic acid, vinyl acetate, 2-butene acid, ethylene sulfonic acid, hydroxyalkyl acrylate, hydroxyalkyl methacrylate, acryl amide, vinyl pyridine, vinyl pyrrolidone, vinyl carbazole, maleic anhydride and pyromellitic dianhydride. In the present invention, the use of acrylic acid or methacrylic acid is especially desirable to obtain a polymeric material with a chemical resistance and a durable water absorption property.
It is a characteristic feature of the present invention that even if a slight amount of hydrophilic polymer is bound to a polymeric material, an effective improvement in the hydrophilic property of the material can be obtained. As mentioned above, an effective hydrophilicity is improved for a thick molded product even when a weight increase in a polymeric material by grafting is a value much less than 1 wt %. In the treatment of a film material, the weight increase by grafting is more than that of a thick material. In the grafting of a non-woven fabric, the weight increase less than 5 wt % gives a good hydrophilicity. However, the present invention is not limited by these values.
In addition, as monomers with low hydrophilicity such as vinyl monomers e.g., esters of acrylic acids, esters of methacrylic acids, vinyl acetate, styrene, etc. can also be used. The use of only hydrophilic monomers is preferable, but, sometimes, the use of a mixture of a hydrophilic monomer and a low hydrophilic monomer increases the percentage of grafting and as a result, the hydrophilic monomer residues in the graft can improve a hydrophilicity of the treated polymer material.
It is desirable that a monomer grafting to a polymer material is made by the heating or the UV irradiation in the presence of initiators. An initiator can be selected from those used in xe2x80x9cthe hydrophilic polymer treatmentxe2x80x9d. When acrylic acid is used as a monomer, a water-soluble initiator such as cerium ammonium nitrate (IV) or potassium persulfate is preferably used. A water-insoluble initiator such as benzoyl peroxide or AIBN is first dissolved in methanol or acetone and the solution is mixed with water. The final solution was used for the treatment. In the grafting by a UV irradiation, a photo-sensitizer such as benzophenone and hydrogen peroxide can be used instead of the initiators mentioned above.
A grafting of monomers is carried out as follows. First, when a water-soluble initiator is used, the amount necessary for the treatment is dissolved in water. If a water-insoluble initiator is used, it is dissolved in an organic solvent such as alcohols and acetone which is miscible in water, and the solution was mixed with an appropriate amount of water, as taking care the precipitation of the initiator. The mixing ratio of water to an organic solvent is not especially limited. For instance, a volume ratio of water/acetone=2/3 is preferable in a mixture of water and acetone, and in a mixture of water and methanol, a volume ratio of water/methanol=1/1. Each of a material finished by an activation treatment and a hydrophilic polymer treatment, and a material finished by a solvent treatment, an activation treatment and a hydrophilic polymer treatment is added in a solution of an initiator, and then a monomer is added in the mixture. It is desirable that the reaction vessel is under a nitrogen atmosphere, but the present treatment can be made under a usual air atmosphere for convenience. A thermal polymerization is carried out by setting a reaction mixture in a thermostatted bath for a given time at a given temperature. For example, it is set for 30 minutes to 6 hours at 80xc2x0 C. When a polymer material is not sunk in a reaction mixture, it is desirable that the material is sunk in the reaction mixture by putting an appropriate glass plate or vessel on it. On the other hand, in the case of a photo-polymerization, a Pyrex glass-made reaction vessel involving a reaction mixture is irradiated by an UV light for 30 minutes to 6 hours at 30xc2x0 C. Various UV lamps are available, for instance, a high pressure mercury lamp, H400P produced by Toshiba Co., Ltd. is preferably used. UV light of about 360 nm monochromated by a filter is applicable, but a whole range of UV light from a UV lamp can also be used. A preferable distance between a reaction vessel and a light source is from 10 cm to 30 cm. When a polymer material is not sunk in a reaction mixture, an appropriate glass plate or vessel is put on it for sinking the material in the reaction mixture.
When a reaction is finished, a polymeric material is taken out of the reaction mixture and is washed with water or an aqueous detergent solution, rinsed well with water and dried. An example of a typical mixing of the reactants is given as follows; a polymeric material 40-80 g, an initiator 0.10-1.0 g and a solvent (mainly, water) 400 ml-800 ml.
As an example of a monomer mixture including a hydrophilic monomer, a mixture of acrylic acid 8 volume and methyl methacrylate 2 volume is applicable. When vinyl acetate or styrene is used, a hydrolysis or a sulfonation should be carried out to improve the hydrophilicity after the grafting.
(Applications)
Properties such as hydrophilicity, water absorption property, water retention property, adhesion property and chemical resistance, etc. are extremely improved in a polymeric material treated by the present invention. The polymeric materials improved by the present invention can be used for many applications because of their characteristic properties. As an adhesion property of a polymeric material is improved, for example, it can be bonded to paper, wood, metal, etc. with general adhesives such as starch, poly(vinyl acetate), epoxy resin, and poly(cyanoacrylate), etc. The present invention is applicable for materials which are necessary for an adhesion property. Furthermore, the present invention is effective for the improvement of polyolefins such as polypropylene and polyethylene whose improvement is known to be difficult and other many kinds of polymeric materials. The water absorption property of a non-woven fabric of a polyolefin or that of a mixture of a polyolefin and another polymer can be improved to give water absorption of 7 to 10 times as much as the original weight. In addition, the improved materials give a good adhesion property and resistances to alkalis, acids and oxidation.
Several applications are described below, but still other applications are also possible.
(1) Battery Separators
The polymer materials improved by the method of the present invention, especially non-woven fabrics of polyolefins such as polypropylene and polyethylene or non-woven fabrics of a mixture of polyolefins and the other polymers are very suitable for battery separators because they give excellent properties in water absorption, adhesion property, resistances to alkalis, acids and oxidation. They give a water absorption ability of 7 to 10 times as much as the original weight and a good absorption ability of electrolytic solutions.
(Alkali Battery Separators)
As alkali battery separators are excellent for a charging-discharging property, an overcharge-overdischarge property and have a long life-time and a repetitive use, they are extensively used in a lot of electronics which need a small size and light weight. The battery with higher capacity is expected. These characteristics of the alkali battery largely depend on the property of the battery separator. The following requirements are desirable for alkali battery separators; an affinity to electrolytic solutions (alkali solutions), a large liquid-absorption rate, a good liquid-retention ability, resistances to alkalis and acids which are durable for the repetitive charge/discharge process, an electric insulation to prevent a short-circuiting, a low electric resistance when they absorb electrolytic solutions, a good permeability for passing gas and ions released in batteries, a thin size suitable for small batteries, a uniform thickness, and a high tensile strength, etc. Non-woven fabrics of polyolefins improved in hydrophilic property and resistances to alkalis and acids are preferable for battery separators satisfying these requirements.
(Lead Storage Battery Separators)
An application for a lead storage battery is explained below.
Lead storage batteries are extensively used for cars and machines because they have a good charge/discharge property, a good overcharge-overdischarge property and a long life time, and they can be used repeatedly. A production of a lead storage battery with a large capacity is expected. These characteristics for a lead storage battery largely depend on the property of battery separators. The following requirements are desirable for lead storage battery separators; an affinity to electrolytic solutions (an aqueous sulfuric acid solution of about 40 wt %), a large liquid-absorption rate, a high liquid-retention property, resistances to alkalis and acids, durability in repeated charge/discharge processes, an electric insulation to prevent a short-circuiting, a low electric resistance when they absorb electrolytic solutions, a good permeability for passing gas and ions released in batteries, a thin size suitable for small batteries, an uniform thickness, and a high tensile strength, etc.
At present, non-woven fabrics containing glass fiber is used for a separator of a lead storage battery. Separators of a mixture of glass fiber and cellulose fiber bounded with a resin are also proposed (Japanese Laid-Open Patent Publication No. S59-73842 (1984)), and the following separator is also proposed; a mixture of powder of inorganic materials and a glass fiber is further more mixed with an acid-resistant synthetic fiber, and which are bound by a resin binder (Japanese Laid-Open Patent Publication No. H8-130001 (1996), Japanese Laid-Open Patent Publication No. H11-260335 (1999)). These separators are heavy and expensive. In addition, there is a problem that the resin used for the binding is exfoliated. On the other hand, a lead-storage battery separator made of non-woven fabric of polyolefins gives a low-cost, a lightweight, and a high mechanical strength. When a separator made of synthetic pulps (non-woven fabrics of polyolefins) impregnated with a surfactant (Japanese Laid-Open Patent Publication No. H5-86562) is used, the surfactant is released in use and the absorption property of an electrolytic solution of the separator is decreased. An acid battery separator was prepared by an addition polymerization of a hydrophilic monomer and polyethylene glycol diacrylate to a synthetic pulp of polyolefins (Japanese Laid-Open Patent Publication No. S62-268900 (1987)). It was described that ammonium persulfate was used as an initiator and any usual methods for polymerization could be employed. However, it is impossible to bind another polymer to polyolefins by the usual polymerization methods proposed in this patent. It is considered that the polymer resin obtained by the polymerization of a monomer seemed to be impregnated into the synthetic pulp of polyolefins and the mixture made solidification. In this case, the long lifetime of the separator can not be expected because the polyolefin fibers should be separated from the polymer resin by the repeated charge/discharge process in the battery.
Thus, the present invention has been carried out to prepare a lead storage battery separator which gives no problems of separators used so far, a lead storage battery separator which gives a high absorption property of electrolytic solutions, resistances to alkalis and acids, a low-cost, a lightweight and a high mechanical strength, and these properties give an excellent durability because its hydrophilicity was made by a real chemical bonding.
(Non-Woven Fabrics for Battery Separator)
Non-woven fabrics for a battery separator prepared by the present invention are explained below. Webs for non-woven fabrics are not especially limited. Polyolefin resins are used as main materials for webs; non-woven fabrics prepared by various dry methods such as a spun bond, melt blow, spun lace, card, sintering, needle punch, cross layer, random weber, air-foaming and air-ray, or non-woven fabrics made by a wet paper machine, or woven fabrics made with warps and wefts are applicable. In addition, their laminates or bonded fabrics are also available.
A wet paper machine method has an advantage that fibers with various diameters or several kinds of fibers are mixed together at an arbitrary mixing ratio. Namely, fibers with various forms such as a staple form and a pulp form and fibers with various diameters from a fine fiber below 7 xcexcm to a thick fiber are available in this method. This method gives webs of very excellent characteristics as compared with the other methods. On the other hand, as the spun bond method and the melt blow method give non-woven fabrics made of fine fibers, a separator made of these non-woven fabrics is favorable for preventing an electrical short circuit between a positive pole and a negative pole in a battery. Especially, to improve a fine structure of a separator, polyolefin fibers with a diameter of 0.1 xcexcm to 15 xcexcm are preferable, and the laminate of a spun bond non-woven fabric and a melt brow fabric or their bonded materials are preferable for the battery separator.
A unit weight and a thickness of a non-woven fabric suitable for an alkali battery separator can be determined by considering the conditions such as a fiber diameter in a fabric, a retention property for electrolytic solutions, and a fine structure (a property to prevent a small electrical short circuit). As an alkali battery separator, a thin fabric gives a good wettability with electrolytic solutions and is favorable for a miniaturization of a battery. However, when a separator is too thin, it causes problems of a low mechanical strength and an electrical short circuit. In addition, when a separator is too thick or too high in density, it takes a long time to immerse the separator in an electrolytic solution and a problem in a charge and discharge process is caused. Furthermore, when a diameter of fiber in a non-woven fabric is very small, the following advantages are given; an increase in a strength for a needling, a prevention of a small electrical short circuit, an increase in an retention property of electrolytic solutions, and an improvement of a life cycle of a battery, but the following disadvantages are caused; a decrease in a permeability of oxygen generated from a positive pole at a charge process, an increase in an inner pressure of a battery and a degradation of a property of a battery at a rapid charge-discharge process.
As a separator of an alkali battery, a non-woven fabric with a pore size of 1-200 xcexcm, a ratio of vacancy of 30-80 v/v %, a thickness of 20-500 xcexcm, a fiber diameter of 1-100 xcexcm, and a unit weight of 5-100 g/m2 are preferably used. Considering these conditions, an alkali battery separator that has a large wettability with an electrolytic solution, a high retention property of an electrolytic solution and a high permeability of oxygen can be obtained.
On the other hand, a lead storage battery needs an appropriate thickness, a high strength and a large liquid retention property. As a separator of a lead storage battery, a non-woven fabric with a pore size of 1-200 xcexcm, a ratio of vacancy of 30-80 v/v %, a thickness of 500-1200 xcexcm, a fiber diameter of 1-100 xcexcm and a unit weight of 100-300 g/m2 is preferably used.
Batteries (or cells) suitable for the separators prepared by the present invention are as follows. Examples of primary batteries are an alkali-manganese battery using an alkaline electrolytic solution, a mercury cell, a silver oxide cell, an air cell, a silver chloride cell, a lithium battery, a manganese battery using an acid electrolytic solution, etc.
Examples of secondary batteries are an alkaline storage battery using an alkaline electrolytic solution (an Edison battery), a nickel-cadmium battery (a Jungner battery), a nickel-hydrogen battery, and a lead storage battery using an acid electrolytic solution, etc. Separators prepared by the present invention can be used instead of paper separators which have been so far used in batteries.
(2) Materials for Wiping/cleansing
At present, a disposable wiping/cleansing material prepared as follows mainly available on the market, that is, a conjugate fiber made with polyester fiber, polyolefin fiber and other synthetic fiber is mixed with rayon fiber which gives a hydrophilicity, and then, the mixed material is impregnated with a surfactant. When the disposable cleansing/wiping material is made with a polymer material improved in the water absorption property by the present invention, the material gives a lightweight, a high mechanical strength, a high absorption property of water and an aqueous surfactant solution and durability in use. It can be used repeatedly several times by washing with water.
(3) Water-Absorption Material
A material with a water absorption property prepared by the present invention is represented.
(4) Water Retention Material
A hydrophilic polyolefin non-woven fabric improved by the present invention is useful for a water retention material which is available for supplying water to plants. To prepare a water retention material, the material of woven fabrics, non-woven fabrics, fibers, and cut disposable fibers are available. The diameter of component fibers in these materials is preferably from 10 xcexcm to 500 xcexcm for convenience.
(5) Medical/Sanitary/Cosmetic Supply
For example, diapers, sanitary supplies, bandages, gauze, sanitary napkins, disinfecting patches/tapes, cosmetic supplies for cleaning/cleansing/face packing and padding, etc. are given. In addition, as the polymer materials improved by the present invention have a good affinity to a human body system, they are available for many kinds of medical accessories or supplies. For instance, vascular grafts, artificial joints, tube/thread/plate-like polymer materials, catheters, tubes or other items for draining, body fluid absorbing materials, contact lenses, lenses for goggles, bandages of synthetic fibers and instillation accessories are given.
The inner part of disposable diapers or sanitary supplies contains materials having a water absorption property which are made of pulp, starch and polyacrylic acid, etc. and the outside part of them is covered with a material having a water repellency which prevents the passing of urine, water and blood, etc. and the surface of the inner part is covered with polyolefin non-woven fabrics with a hydrophilic property. Water generated from a body is passed through the inner hydrophilic non-woven fabric and absorbed by the water absorption material. A hydrophilic polyolefin non-woven fabric is the most preferable material because it is strong and not easily broken in water. However, the method to give a hydrophilicity to the non-woven fabrics used in the inner material is only to dip them in surfactants or water-soluble reagents, which is easily removed by rinsing in water. In addition, the effect of surfactants to skins is worrying. Thus, a cheap, easy and durable method to improve a hydrophilicity of a polymeric material is expected. Polyolefin materials improved in a water absorption/retention property which are prepared by the present invention are the most favorable for the fabrics used for the cover of the inside of disposable diapers and sanitary supplies. In addition, polymer materials with a high water absorption property which are prepared by the present invention are also available for water absorption materials used as an inner pad of disposable diapers or sanitary supplies. The improved materials by the present invention are light in weight, mechanically strong and safety, and give a durability for repeating uses. In addition, polymer materials obtained by the present invention give a hydrophilic property or a water absorption property, and they are light and strong. As they can be impregnated with detergents, chemicals and adhesives, they are available for gauze, fiber products for wiping, disinfecting cloth patches or tapes, and the other cosmetic supplies. When they are used for disposable medical/sanitary/cosmetic supplies, each of a woven fabric or a non-woven fabric is preferably used as a material""s form, and the unit weight and thickness of the material are appropriately selected. A diameter of fibers in a non-woven fabric, 1-500 xcexcm is easily used.
(6) Internal Materials for Clothing/bed/bedclothes
The polymer materials having a hydrophilicity and a water absorption property obtained by the present invention are light in weight and mechanically strong. When their water absorption ability is controlled in a preferable extent, they are suitable for fiber products of clothes and an inner material for beds and bedclothes.
(7) Filter Mediums
Filter mediums of porous films made of polyolefins, polysulfone, and polyester, etc. give a mechanical strength and a low hydrophilicity as compared with paper filters. They are not available for the filtration of aqueous solutions because of the low hydrophilicity. At present, they are coated with surfactants or water-soluble polymers in order to improve the hydrophilicity. However, the hydrophilic layer of the filters is non-durable and is easily dissolved in filtrates in the process of filtration. When the hydrophilic treatment of the present invention is applied for the filter mediums, it is expected that filter mediums with a durable water absorption property are obtained.
(8) Materials for Microbial Culture Medium
As water retention materials obtained by the present invention give a high water absorption property, a large mechanical strength, and a large microbial fertility, they are suitable as the materials of a microbial culture medium. Various forms of materials such as woven fabrics, non-woven fabrics, fibers and cut disposable fibers are available. A diameter of component fibers in these materials is preferably from 10 xcexcto 500 xcexcm.
(9) Members of Writing Materials
Most of writing materials such as various ball-point pens with water-soluble ink, felt-tip pens, brush pens and fountain pens contain members made of plastics. At present, plastic materials made of ABS resin, polyester and nylon are treated by a plasma treatment or a corona discharge treatment to improve the affinity to water-soluble ink and they are mainly used as members for writing materials. Instead of these materials, polyolefins such as polypropylene and polyethylene are improved and can be used for the members of writing materials, which give advantages of lightweight, safety, etc. The present invention makes it possible to improve the hydrophilicity of usual hydrophobic plastic materials and to use the improved materials for the plastic members of writing materials, which have a good absorption/retention property of water-soluble ink; for example, hydrophilic members such as ink-tanks, ink-collectors, heads of brush pens, ink-absorbing polyester fibers and polyurethane sponges can be prepared.
(10) Orthodontic Brackets
The present invention can improve an adhesion property of polymer materials. As this improvement is available for various materials which need a good adhesion property, such as composites and fibers used for fiber reinforced plastics, it is also available to improve the adhesion property of orthodontic brackets.
(11) Polymer Composites
The adhesion property of fibers mixed in polymer composites or in fiber reinforced plastics is improved and the fibers are applied for making strong polymer composites. The adhesion property of fibers mixed in polymer composites or in fiber reinforced plastics are improved by the present invention and they are applied for making strong polymer composites.
(12) Synthetic Papers
Synthetic papers made of polymer materials such as polyolefins (polyethylene and polypropylene, etc.) and polyester, etc. are whitened by adding air bubbles or fillers, and they are used as alternative papers. The present invention can improve a hydophilicity, an adhesion property and a printing property of synthetic papers.
(13) Materials with Improved Adhesion Property
In addition to the orthodontic brackets and the fibers used for composites, the property of the other materials such as various polymer films and molded materials is also improved. The adhesion property between the same kind of materials or different materials can be improved.
(14) Application of Hydrophilic Film
The present invention gives a high hydrophilicity to polymer films of polyolefins and polyester, etc. For instance, water-absorption polyester films give a good adhesion property and a wettability with water, and they show an anti-fogging property when they are put on glasses and mirrors.